One’s teeth on helical gears are cut at an angle to the face of the apparatus. When two teeth on a helical gear system engage, the get in touch with starts at one end of the tooth and steadily spreads as the gears rotate, until the two teeth are in full 
engagement.
This gradual engagement makes helical gears operate a lot more smoothly and quietly than spur gears. Because of this, helical gears are found in almost all car transmissions.
Due to the angle of one’s teeth on helical gears, they create a thrust load on the gear when they mesh. Products that use helical gears have bearings that can support this thrust load.
One interesting thing about helical gears is that if the angles of the gear teeth are right, they may be mounted on perpendicular greenhouse reducer shafts, adjusting the rotation angle by 90 degrees.